mineral

Satin Spar (Selenite)

Gypsum (Calcium Sulfate Dihydrate) - CaSO4·2H2O

Hardness: 2 on Mohs scale (scratchable with fingernail). Color: White to pearly translucent. Luster: Silky or pearly. Crystal Structure: Monoclinic, typically fibrous. Cleavage: Perfect in one direction, though this fibrous variety splits into threads.

Hardness: 2 on Mohs scale (scratchable with fingernail)
Color: White to pearly translucent
Luster: Silky or pearly

Identified March 16, 2026More mineral →

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Physical properties

Formation & geological history

Formed as an evaporite mineral in sedimentary environments, typically where salt water has evaporated. It occurs in clay beds and as a deposit from volcanic gases or in hydrothermal veins.

Uses & applications

Used in the manufacture of plaster of Paris, wallboard (drywall), soil fertilizer, and as a filler in paper and paints. Popular in metaphysical crystal collecting as wands or carved ornaments.

Geological facts

Satin Spar is a fibrous variety of gypsum often confused with Selenite (which is clear and plate-like). It exhibits a 'cat's eye' effect or chatoyancy due to its parallel fibrous structure.

Field identification & locations

Identify by its extreme softness (the fingernail test is definitive) and its distinctive silky, fiber-like appearance. Common in the UK, Morocco, and the USA (notably Utah and New Mexico).

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